The effects of beta-radiation on sister-chromatid exchanges in cultured human lymphocytes

Sister chromatid exchanges in lymphocytes of nuclear medicine physicians

OBJECTIVE

The aim of this study was to assess whether occupational exposure to chronic, low doses of Iodine 131 (I-131) and Technetium 99m (Tc-99m) may lead to genotoxicity. Medical personnel occupied in nuclear medicine departments are occupationally exposed to low doses of I-131 and Tc-99m. The determination of the frequency of sister chromatid exchanges (SCEs) and of cells with a high frequency of SCEs (HFC) is considered to be a sensitive indicator for detecting genotoxic potential of mutagenic and carcinogenic agents. Therefore, we examined peripheral lymphocytes from nuclear medicine physicians for the presence of both SCE and HFC.

METHODS

Sixteen exposed nuclear medicine physicians (non-smokers) were compared to 16 physicians (non-smokers) who had not been exposed to chemical or physical mutagens in their usual working environment at the same hospital.

RESULTS

A statistically significant difference was found between SCE frequencies and HFC percentages measured in lymphocytes from the exposed and control groups.

CONCLUSIONS

The present observation on the effect of chronic low doses of I-131 and Tc-99m indicates the possibility of genotoxic implications of this type of occupational exposure. Hence, the personnel who work in nuclear medicine departments should carefully apply the radiation protection procedures and should minimize, as low as possible, radiation exposure to avoid possible genotoxic effects.

Sister chromatid exchange analysis in patients exposed to low dose of iodine-131 for thyroid scintigraphy

To determine the genotoxic risk associated with diagnostic exposure to low doses of iodine 131 (131I), sister chromatid exchange (SCE) analysis was performed in lymphocytes of 18 non-smoking women who received 370 kBq (10 microCi) intravenous 131I sodium iodide as an adjuvant for scintigraphy for diagnosing thyroid nodularity. SCE frequencies were measured before and after 131I administration. SCE results in the pre-treated phase were regarded as control. Although SCE values 24 h after 131I administration did not show a significant increment (p > 0.05), there was a significant increase 72 h after treatment (p < 0.05). These results indicate that genetic damage might be induced by low dose of 131I.

Cytogenetic effects of an alkyl-lysophospholipid derivative in human peripheral lymphocytes exposed in vitro and in vivo

Chromosome analyses were carried out in human lymphocytes exposed to an antitumor alkyl-lysophospholipid (ALP) in vitro and in vivo. There was no evidence for a significant clastogenic effect or incidence of an increased sister-chromatid exchange (SCE) after short-term and long-term treatment of unstimulated or stimulated lymphocytes with concentrations of 0.1-50 micrograms ALP per ml. Cell proliferation was delayed after G0 exposure to 50 micrograms/ml. Although no ALP monotherapy was present for 3 cancer patients examined before and during ALP treatment with accumulated doses of 15-516 mg/kg, the cytogenetic data were in accord with the negative experimental results.

Can 3H-uridine-induced sister chromatid exchange be used as a measure of transcriptional activity of chromosomes?

In order to test the validity of using 3H-uridine-induced chromosome damage as a measure of the transcriptional activity of chromosomes, experiments were performed to examine the mechanism by which 3H-uridine induces sister chromatid exchanges. DON and B14FAF28 Chinese hamster cells exposed to 3H-uridine showed a dose-dependent increase in SCE frequency, whereas unlabelled uridine produced no increase. 3H-uridine labelling in the presence of increasing concentrations of unlabelled uridine eliminated this increase in a concentration dependent manner. Competition between 3H-uridine and other unlabelled pyrimidines (thymidine and cytidine) was equally as effective; however, unlabelled hypoxanthine had no effect on 3H-uridine-induced SCEs. This suggested that 3H-uridine caused SCEs after interconversion into deoxycytidine followed by incorporation into DNA. Significant incorporation of 3H into DNA was confirmed by direct comparisons of label in the DNA and RNA fractions, and about 90% of this label was found to be in the cytosine fraction of hydrolysates. We therefore conclude that 3H-uridine produces chromosome damage because of the incorporation of a tritiated conversion product into DNA, rather than by exposure of transcriptionally active DNA to 3H-uridine-labelled RNA. We suggest therefore, that the results of earlier experiments, in which 3H-uridine chromosome damage has been used to assay the transcriptional activity of chromosomes, may need to be reinterpreted.

Variation in the sensitivity of human lymphocytes to DNA-damaging agents measured by sister chromatid exchange frequency

Peripheral blood lymphocytes from normal donors were exposed to mitomycin C 0.01 microgram/ml, proflavine 0.4 microgram/ml, and 3H-uridine 3.7 Bq/ml and analyzed for the incidence of sister chromatid exchanges (SCEs). Cellular proliferation in the presence of these three agents was also measured by determining the number of first, second, and third divisions present. All donors showed a significant increase in SCE following treatment with mitomycin C, whereas only two-thirds showed an increase following treatment with proflavine and only half, with 3H-uridine. The variation in response was not related to either the age or sex of the donor. Cellular proliferation was likewise affected by all three agents. 3H-uridine caused the greatest reduction in the number of metaphases. There was no correlation between the sensitivity to one agent and another, nor was there any correlation the reduction in the number of metaphases and the increase in the number of exchanges.

A comparison of induced sister chromatid exchange levels in Chinese hamster ovary cells and cultured human lymphocytes

Human lymphocytes and Chinese hamster ovary cells were exposed to DNA damaging agents for two cell cycles, and the induced sister chromatid exchange (SCE) rate was compared. CHO cells showed a significant increase in SCE following treatment with bleomycin and vincristine whereas human lymphocytes did not. Both CHO cells and lymphocytes showed an increase in SCE with 5-bromodeoxyuridine (BrdUrd) and tritiated uridine (3H-Urd) but the increase was greater in CHO cells. SCE levels were similar after exposure to proflavine and colcemid did not increase the exchange frequency in either cell type. Apparently CHO cells are more sensitive than human lymphocytes to the actions of bleomycin, vincristine, BrdUrd, and 3H-Urd. SCE analysis in response to mutagens and carcinogens should therefore be based on more than one cell type.

Sister chromatid exchange (SCE) and structural chromosome aberration in mutagenicity testing

Data from previous studies published on the induction by mutagens of sister chromatid exchanges (SCEs) and structural chromosome damage were compared qualitatively and quantitatively. Although a good correlation between the incidence of both cytogenetic phenomena has been pointed out in many previous publications, about 30% of the agents for which comparable data were available yielded non-corresponding qualitative results concerning both indicator effects. However, even in groups with good qualitative agreement distinct quantitative differences indicated different molecular mechanisms of the formation of SCEs and breaks. Additional information supporting the importance of these differences for the validity of both indicator systems has been derived from the results obtained using strong clastogens exhibiting a low or no SCE-inducing activity and vice versa, from special observations on chromosomal breakage syndromes, and from studies on the action of known co- and anti-clastogens on SCE-induction by chemical mutagens. As a result, it has been suggested that the SCE-technique should be considered as a valuable additional method for cytogenetic mutagenicity testing, which, however, is not adequate to replace the classical methods of analysis of structural chromosome damage.